While there are a few disease entities that can cause a pressure sensation in the eyes besides dry eye syndrome, like orbital inflammation, or glaucoma, these are much less likely to cause this pressure than dry eye syndrome is.
Dry eyes can be due to many different factors. Different medicines such as psychiatric medicines, antihistamines, cold medicines and others can contribute to dry eyes. Allergies in the eyes can also contribute (make dry eyes worse). Some people have an innate deficiency in making their own tears (these people may also have other dry mucus membranes, such as their mouth, nasal passages, or genitalia); this is Sjogren's syndrome. Many people have an inflammation in the eyelids called blepharitis which causes the tear film that is supposed to coat the front of the eye to not function as well, and then the eyes dry out. People with blepharitis sometimes have morning tearing, burning, and often eyelash mattering. People with dry eye syndrome in general have intermittent blurring when they use their eyes heavily in activities such as reading, watching TV, computer use or driving.
Because blepharitis is so under-diagnosed and the treatment for it is relatively benign and something that won't hurt your eyes, you might consider starting this treatment, while concurrently continuing artificial tears. In order to treat blepharitis, everyday in the morning you should do two things: 1. hot compresses and 2. eyelid scrubs. You should do hot compresses for 5-10 minutes over each eye at the same time. It should be as hot as you can tolerate without burning your skin, massaging the eyelids while they are on there. Then, use either commercially available preparations or a dilute baby shampoo solution to scrub your eyelashes on all 4 eyelids. The commercially available preparations are called Ocusoft or Sterilid which are both over-the-counter eyelash scrubbing treatments. These cost more money but are quicker to use. Otherwise, the cheaper alternative is the dilute baby shampoo (4-5 drops Johnson's shampoo in 1/4 cup warm water), you will take the wipe (or dip a qtip in the dilute baby shampoo solution) and use that to scrub right on the eyelashes of each eyelid for 15 seconds. That will take 60 seconds when done to all 4 eyelids. The scrubbing is done right on the eyelid margin, where the eyelashes come out. After that, just splash some water on the eyes and you're done.
It does take about 3-4 weeks of doing this consistently every day before it really kicks in, so don't stop it thinking it's not working. Also the eyes are still significantly dry during this 3-4 weeks so use the artificial tears you bought 4x/day in both eyes (one drop per application). After 4 weeks you should be able to start tapering off of the tears to as you need them.
Just doing the artificial tears, hot compresses and eyelid scrubs alone would likely start to help you after three or 4 weeks--but remember it could take this long of doing it everyday before you see a significant effect, so don't stop it thinking it's not working.
If you are a person that doesn't make their own tears very well, like someone with Sjogren's syndrome, then you may also benefit from a prescription drop called Restasis, which actually modulates a person's immune system to help them make more of their own tears. This drop actually requires constant usage on a daily basis for up to 10-12 weeks before its effect kicks in (takes awhile to change the immune response in the body).
Because there are numerous reasons for dry eye, if not all the reasons that exist in one patient are treated, it can seem as though the ones that are being treated are providing no benefit. If you've tried these recommendations and still don't feel better then you should consider seeing a corneal specialist for a dry eye evaluation.
Does that all make sense?